Promote beta to SQL

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The beta code path is feeling stable enough at this point - let's make the switch - however I think fixing #60 first is important though

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The switch will need testing with the docs infra (where we embed fiddles into the pages using a slightly different UI), just in case there are some surprise snags there https://github.com/xtdb/xtdb/tree/main/docs

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Let's keep XTQL (and the in-process code path) for now, so we don't break a tonne of stuff and limit our demonstration capability.